1. Field of the Invention
This invention relates generally to wireless telecommunication. More particularly, it relates to 3GPP (3rd Generation Partnership Project) location continuity using long term evolution (LTE)/System Architecture Evolution (SAE) access.
2. Background of the Related Art
Long Term Evolution (LTE) of the 3rd Generation Partnership Project (3GPP) is the next stage of wireless communications, introduced in the 3GPP Release 8. This 3GPP project improves the Universal Mobile Telecommunications System (UMTS) mobile phone standard to provide an enhanced user experience and simplified technology for next generation mobile broadband. Much of 3GPP Release 8 is oriented towards a 4th Generation (4G) mobile communications technology and an all-Internet Protocol (IP) architecture system. A copy of “3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Mobile Application Part (MAP) Specification; (Release 8)”, 3GPP TS 29.002 V8.1.0 (2007-03), is filed herewith by way of Information Disclosure Statement, and is incorporated by reference into this background in its entirety.
SAE is an evolution of the General Packet Radio Service (GPRS) core network, but it's an all-IP network. The main component of the SAE architecture is the Evolved Packet Core (EPC), also known as the SAE Core. The EPC will serve as equivalent of GPRS networks (via the Mobility Management Entity, Serving Gateway and PDN Gateway subcomponents). The subcomponents of the EPC include a Mobility Management Entity (MME), a Serving Gateway (S-GW), and a Packet Data Network Gateway (PDN-GW).
The MME is the key control-node for the LTE access-network. It is responsible for idle mode UE (User Equipment) tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation process and is also responsible for choosing the SGW for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation. It is responsible for authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to UEs. It checks the authorization of the UE to camp on the service provider's Public Land Mobile Network (PLMN) and enforces UE roaming restrictions. The MME is the termination point in the network for ciphering/integrity protection for NAS signaling and handles the security key management. Lawful interception of signaling is also supported by the MME. The MME also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME from the SGSN. The MME also terminates the S6a interface towards the home HSS for roaming UEs.
The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNB handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN). For idle state UEs, the SGW terminates the DL data path and triggers paging when DL data arrives for the UE. It manages and stores UE contexts, e.g. parameters of the IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception.
The PDN provides connectivity to the UE to external packet data networks by being the point of exit and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one PDN for accessing multiple PDNs. The PDN performs policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening. Another key role of the PDN is to act as the anchor for mobility between 3GPP and non-3GPP technologies such as WiMAX and 3GPP2 (CDMA 1× and EvDO).
Depending on the deployments of a telephony network operator, regional requirements, reliability of emergency services, and other operational reasons, it is very common in North America that a telephony network (wireless or fixed line) is divided into different emergency service regions. The emergency location services of the service regions may be provided by a single emergency location service provider, or very often by multiple emergency location service providers. Sometimes load balancing and redundancy requirements of emergency location services require multiple emergency location service providers for a network.
Location Retrieval Function (LRF) is a functional entity that handles the retrieval of location information for a user entity (UE).
For the existing 3GPP circuit switched (CS) based emergency location services defined in 23.271 of the 3GPP Specification, when a location estimate is required for a target user equipment (UE)/mobile station (MS) with an established emergency call in a state of inter-visited mobile switching center (VMSC)/MSC server handover, all location request related messages are sent via Mobile Application Part (MAP)/E interface piggy-backed in MAP_FORWARD_ACCESS_SIGNALLING and MAP PROCESS_ACCESS_SIGNALLING between the visited and serving MSCs/MSC servers. The serving GMLC only needs to communicate with an anchor MSC/MSC server during an emergency call.
In the Release 9 version of an SAE network, an IP Multimedia Subsystem (IMS) emergency call will be provided using the underlying IP Bearer established over E-UTRAN/UTRRN access network. It is very important to note that the IMS Emergency procedure defined in 23.167 is independent from the procedures of SAE/GPRS, including the Control Plane Location Service procedures, the only interworking function between these two service domains resides in the serving LRF. Some challenges/issues have been identified when there are multiple IMS emergency location service providers (i.e. multiple LRFs) in a network:
There is not a signal tunneling mechanism (like the one in the CS domain) available, the serving LRF needs to know the current serving location server (GMLC/MPC for control plane or E-SLP for user plane) and the serving node after a handover (either PS-PS or PS-CS) crossing the service regions of the emergency location service providers.
Due to the fact that IMS domain and signaling domain of U-TRAN Access and Location Services are decoupled, it is possible that IP Bearer has been established and emergency NI-LR has been initiated, but a handover occurs crossing the service regions of the emergency location service providers before an IMS Emergency call is initiated. Or it is possible that the IP bearer of an emergency IMS call would not yet be released after the IMS emergency call is terminated, another emergency call is placed using the same bearer (but where the emergency location area would be different).
MME Pool may be deployed; the MME may be dynamically assigned. But the inventor herein appreciates that there is not a fixed mapping between E-Cell and MME, thus the serving LRF cannot use the serving E-Cell ID that is available via IMS signaling to determine the serving node and serving location server after a handover crossing the service areas of emergency location service providers.
It has been noted that User Plane Location Service using OMA SUPL may also be used for IMS emergency location services, but there are limitations of OMA SUPL 2.0. The recommended solution preferably should support handover scenarios from a UP based emergency location service provider to a CP based emergency location service provider, but the requirements for an additional User Plane are not in the scope of 3GPP. Although in 3GPP Rel-9, the scope of emergency location continuity is limited to one single carrier, and the scope of IMS emergency voice call continuity (VCC) is limited to the PS to CS direction only. (Voice call continuity (VCC) is an IMS service standardized in 3GPP TS 23.206. Using VCC, ongoing calls can be switched from wireless to WiFi at any time using 2G/3G/WiFi handsets, or transferred at any time to another handset.)
Using current technology, emergency location services associated with IMS emergency calls may be interrupted when there are multiple LRFs deployed in the network. In such a case, a public service access point (PSAP) would not be supported following a handover of an IMS emergency call.